1. Field of the Invention
The present invention generally relates to an optical pickup of an optical disk drive, and more particularly to an optical lens posture adjusting mechanism for an optical pickup.
2. Related Background Art
An example of the structure of an optical pickup of an optical disk drive is shown in FIG. 5. Reference numeral 1 represents a laser diode which emits a laser beam. The laser beam emitted from the laser diode 1 passes through a diffraction grating 2, is reflected by a beam splitter 3, and is incident upon a collimator lens 4. The laser beam is converted into a parallel beam by the collimator lens 4, reflected by a mirror 5, and is incident upon an objective lens 6.
The laser beam incident upon the objective lens is converged on a signal recording surface of an optical disk 9. The laser beam applied to the optical disk 9 is reflected by the signal recording surface, and becomes incident upon the beam splitter 3 via the objective lens 6, mirror 5, and collimator lens 4 along the pass opposite to the incident laser beam. Most of the laser rays incident upon the beam splitter 3 transmit the beam splitter 3 and are incident upon a convex lens 7. The laser beam is converged by the convex lens 7 onto a light receiving surface of a photodiode 8 and the information recorded on the optical disk 9 is read.
In order to correctly read information by such an optical pickup, it is necessary to make the objective lens apply a laser beam to an optical disk in the direction perpendicular to the recording surface thereof and be reflected by the recording surface in the perpendicular direction, and to make the reflected laser beam be converged to the photodiode 8. To this end, the optical axis of a laser beam reflected by the objective lens is required to be coincident with the optical axis of a laser beam guiding optical system. An example of a conventional objective lens posture adjusting mechanism is shown in FIG. 4. Reference numeral 10 represents an optical system support base which supports an optical system excepting an objective lens. An objective lens support base 11 is mounted with a printed circuit board 13 by screws. The printed circuit board 13 resiliently supports a lens holder 6a by means of four resilient members 14.
Two pairs of confronting yokes 11b and 11c are mounted on the objective lens support base 11. Magnets 12 are mounted on the yokes 11c. The objective lens 6 is secured to the lens holder 6a, and the yokes 11b are inserted into holes formed in the lens holder 6a. A tracking coil and a focussing coil for interacting with a magnetic field generated by the yokes and magnets are secured to the lens holder 6a.
A spherical convex 11a is formed at the objective lens support base 11, and a spherical concave 10a in surface contact with the spherical convex 11a is formed at the optical system support base 10. The objective lens support base 11 is aligned with the optical system support base 10 by making the spherical convex 11a in surface contact with the spherical concave 10a, and held in position by screws 17 and 15.
As specifically shown in FIG. 5, the screws 17 are inserted into washers and holes formed in the optical system support base 10, and threaded into tapped holes formed in the objective lens support base 11. In the above manner, the objective lens support base 11 is attracted toward the optical system support base 10 by the force of the coil spring 16, and the spherical convex 11a is maintained in tight contact with the spherical concave 10a.
By adjusting the threading amount of two screws 17, the rotary angle of the objective lens 6 about the X- and Y-axes shown in FIG. 4 is controlled. A laser beam entering the objective lens 6 passes through holes formed in the spherical convex 11a and concave 10a at the centers thereof.
The above-described object lens posture adjusting mechanism of an optical pickup adjusts the rotary angle of the objective lens about the X- and Y-axes by using two screws. However, adjustment is not easy because the objective lens rotates about both the X- and Y- axes even if one of the screws is rotated.
Furthermore, the spherical convex 11a is formed on the central bottom surface of the objective lens support base 11, so that it is difficult to observe the contact conditions of the surfaces of the spherical convex 11a and concave 10a. If a surface contact is not perfect, a sufficient contact force at the bonded surfaces after the adjustment cannot be ensured. Also, there is a problem that adhesive agent is difficult to be applied to the whole contact surfaces.
Still further, space for the mirror is not available because the hole formed in the spherical convex 11a is circular. Therefore, the mirror is required to mount under the spherical convex, thickening the optical pickup.